the biggest way I can think of is by word of mouth. You can talk to friends, associates, family, etc. You could create some little signs and put them in your car window (maybe others cars to). If your a member of Facebook and/or Twitter you can set your status to promote your site. I hope I have given you a few good ideas.
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Try posting some of your designs in online logo galleries like http://www.logopond.com, search logo design on Twitter and Facebook, and answer questions in fourms like this one. Make sure to leave a link to your website or portfolio.